JD - Vestibular System Flashcards
What are the main features of the vestibular system (3)?
- Located in the ear
- Important for reflexive movements
- Balance
What does the VS communicate with and control?
Communicates with muscles in neck and head and controls:
- Head position
- Self-motion
- Spatial orientation
What does VS dysfunction result in?
‘Dizziness Disorders’
- E.g Meniere’s disease
Describe the structure of the Vestibular System?
Made up of interconnected chambers (vestibular labyrinth)
- Utricle
- Saccule
Semicircular canals:
- Superior
- Posterior
- Horizontal
What is the VS joined to?
The Cochlea
- Has the same fluids as the cochlea
The fluids have the same ionic profiles
- Endolymph (high in K+)
- Perilymph (low in K+)
Name the three types of movement in 3D space detected by the vestibular system?
- Translational (primarily detected by otolith organs)
- Static head tilts (primarily detected by otolith organs)
- Rotational (detected by semicircular canals)
Describe the mechanism of vestibular hair cell activation in stereocilia
Movement from short stereocilia to long opens mechanogated potassium channels, leading to depolarization
What are otolith organs, macula and the otolithic membrane?
- The utricle and saccule are called otolith organs
- The sensory epithelium is called the ‘macula’
- The otolithic membrane is a gel layer with calcium carbonate crystals
Static Head Tilts vs Liner Head Accelerations
Static Head Tilts
Movement of the head backwards and forward has the same effect on the otolithic membrane
Linear Head Accelerations
FORWARD ACCELERATION causes denser otolithic membranes to travel backwards
- Head moves backwards
DECELERATION causes denser otolithic membranes to travel forwards
- Head moves forwards
How are the saccular macula and utricular macula orientated?
The utricular macula is orientated horizontally
- The utricule responds to translational movements of the head in the horizontal plane (left-right) and to side ways head tilts (left right)
The saccular macula is orientated vertically
- The saccule responds to translational movements of the head in the vertical plane (up-down)
What do the utricle and saccule detect?
Utricle detects movements in the horizontal plane
Saccule detects movements in the vertical plane
How is rotational movement detected?
Endolymph flow moves in the opposite direction to Angular acceleration
- Displaces Cupula and results in depolarization (shortest to longest stereocilia)
Head movement from R → L causes Endolymph movement from L → R
- One stereocilia becomes depolarised whilst opposite becomes hyperpolarised
What are 3 outputs of the Vestibular Nuclei (Brainstem)?
→ Output to spinal cord and motorneurons of the limb and torso (descending)
- Maintenance of balance and posture
→ Output to motorneurons of external eye muscles
- Control of eye movement
→ Output to Thalamus (ascending)
→ Cortex
- Perception of motion and self awareness
What is the Vestibulo-ocular Reflex?
A reflex that controls the movement of the eye sockets when the head moves
- The reflexive eye-movement moves the eye in the opposite direction to the head
Acts to stabilise gaze
What is the purpose of the Vestibular-Cervical (VCS) and Vestibular-Spinal Reflex (VSR)? (Descending)
Medial co-ordinates the VCR
- Signals from the semi-circular canal control neck muscles and head position via this pathway
Lateral and Medial nucleus co-ordinates the VSR
- Signals from the otoliths travel to the lateral vestibular nucleus and nerve cells carry signals via the vestibulospinal tract to the spinal cord
